eyed cicadas have also lighter colored costal edges to the front wings and this might be considered a failure to completely darken the wing which at first was white and normally turns darker soon after hatching out from the pupa case. The white eye, however, is of fundamental nature since the normal red eye is one of the earliest areas of the body which stands out against the general whiteness as fiery red and in these two white-eyed individuals the absence of color in the eye dated back beyond the time of transformation.

Thus amidst about five thousand seven hundred cicadas two had white, one black and one chestnut colored eyes. Other collections showed that white-eyed and brown-eyed forms occurred now and then both in this same region and in Roland Park and thus from diverse groups that had been separated a couple of miles for seventeen years at least.

In the assumedly rather uniform and simple conditions of seventeen years of growth under ground there would seem little opportunity for light or other external conditions to exert any such modifying influence as might lead to white in place of red eye. Regarding the two periods of life, the short one as active larva getting into the ground and the concealed egg in the wood, as opposed to the germ life in the active adult, we seem safe in assuming that here as elsewhere the initiative to change in eye color came in the germinal material.

The injury done to trees and shrubs by the adult females in laying is not only the immediate death of important twigs when too severely cut by the ovispositor but in the leaving of wounds that may later cause injury. While the severely injured twigs may fall off soon and thus often lead to the failure of the cicada eggs from drying, the partly injured twig remains and begins to heal over, but this overgrowth rarely overtakes the young before it comes out of the wound. The following summer, 1920, many of the injured twigs were healed over more or less completely. Nevertheless the wood had been so deeply injured that a great many twigs bearing green leaves and such fruits as those of the Norway Maple were wrenched off by storms owing to the internal weakening caused by the previous season by the cicadas.

While the extensive pruning may not cause serious results in many shade trees, the dying off of twigs, the remaining of dead tips and the presence of innumerable wounds is of moment in some fruit trees and in the dogwood the pruning back by the cicadas tended to make considerable changes in fruiting, flowering and proportions of growth, while in some chestnut shoots recovering from dying down after the blight the wounds made by cicadas were placed with reference to new infestations of the blight so as to suggest that the blight had entered through these wounds in the firm young bark.

How serious the loss of sap of roots through long years of cicada sucking may be, remains to be found out.

The almost absolute completeness of the emergence in 1919 is seen in the fact that in 1920 search for these seventeen year locust yielded not one. Even in the region along Charles Street north of University Parkway where in 1919 the cicadas were swept up from the sidewalk in great numbers no cast off shells could be found in 1920 and but one solitary song in this region indicated that there had been an emergence of one of the race this season; all the others having come out in 1919 with practically no lag.

It is the phenomenal uniformity with which all these creatures in a given region run through their long period of growth to emerge within so few days after seventeen years and with so few exceptional hurried or lagging individuals that presents a problem in rhythmic growth of great interest as is also the question as to how far these insects may be guided by sight in the first use of their eyes upon coming from seventeen years of apparent darkness. These and other questions may be approached experimentally if attention is called to this field in time; and fortunately some broods of these insects come out at predictable dates in various parts of the country in different years so that observation can be spread over much of the long interval otherwise lost in any one locality.

THE BIOLOGY OF DEATH.

IN

II-CONDITIONS OF

CELLULAR IMMORTALITY1

By Professor RAYMOND PEARL

THE JOHNS HOPKINS UNIVERSITY

1. ARTIFICIAL PARTHENOGENESIS

N the preceding paper in this series it was pointed out that the germ cells of higher organisms are potentially, and under certain conditions in fact, immortal. What are the conditions of immortality in this case? Are they such as to support the thesis that the processes of mortality are essentially physico-chemical in nature, and follow physico-chemical laws?

The most essential condition of this immortality of germ cells was mentioned, but not particularly emphasized. It is that two germ cells, an ovum and a spermatozoon unite, the process of union being called fertilization. Having united, if they then find themselves in appropriate environmental conditions, development goes on, new germ cells and a soma are formed, and the same process keeps up generation after generation. Now while union of the germ cells is generally and in most organisms an essential condition of this process, it is also true that in a few forms of animal life, mostly found among the invertebrates, development of the ovum can take place without any preceding fertilization by a spermatozoon. The process of reproduction in this case is called parthenogenesis. In a number of forms in which parthenogenesis never occurs normally, so far as is known, it can be induced by appropriate extraneous procedures. The discovery of this extraordinarily interesting and important fact for a number of organisms, and the careful working out of its physico-chemical basis, we owe to Dr. Jacques Loeb, of the Rockefeller Institute for Medical Research. Artificial parthenogenesis may be induced, as Guyer, Bataillon and Loeb have shown in so highly organized a creature even as the frog, and the animal may grow to full size. The frogs shown in Figure 1, while they present much the same appearance as any other frog of the same species, differ in the rather fundamentally important respect that they had no father.

The rôle of a father was played in these cases by an ordinary dissecting needle. Unfertilized eggs from a virgin female were gently pricked on the surface with a sharply pointed needle. This initiation

1Papers from the Department of Biometry and Vital Statistics, School of Hygiene and Public Health, Johns Hopkins University, No. 29.

VOL. XII.-21.

FIG. 1. ARTIFICIALLY PARTHENOGENETIC FROGS. (Loeb.)

of the process of development took place March 16, 1916, in one case, and February 27, 1917 in the other. The date of death was in the first case May 22, 1917 and in the other March 24, 1918.

In the course of Loeb's studies of parthenogenesis in lower marine invertebrates, he became interested in the question of the death of the germ cells which had failed to unite, or having united failed of appropriate environmental conditions. His researches throw light on some of the conditions of cellular death, and on that account they may be reviewed briefly here. He found that the unfertilized mature eggs of the sea-urchin die comparatively soon when deposited in sea-water. The same eggs, however, live much longer, and will if appropriate surrounding conditions are provided go on and develop an adult organism, if they are caused to develop artificially by chemical means or naturally by fertilization. Loeb concluded from this that there are two processes going on in the egg. He maintained, on the one hand, that there are specific processes leading to death and disintegration, and, on the other hand, processes which lead to cell division and further development. The latter processes may be regarded as inhibiting or modifying the mortal process. Loeb and Lewis undertook experiments based upon this view to see whether it would be possible by chemical treatment of the egg to prolong its life. Since in general specific life phenomena are perhaps on the chemical side chiefly catalytic phenomena, it was held to be reasonable that if some substance could be brought to act on the egg, which would inhibit such phenomena without permanently altering the constitution of the living material the life of the cell should be considerably prolonged. The first agent chosen for trial was potassium cyanide, KCN. It was known that this substance weakened or inhibited entirely a number of enzymatic processes in living material, without materially or permanently altering its structure.

It was found that normally the unfertilized egg of the sea-urchin would live in sea-water at room temperature, and maintain itself in condition for successful fertilization and development, up to a period of about twenty-three hours. After that time the eggs began to weaken. Either they could not be successfully fertilized, or, if they were fertil ized, development only went on for a short time. After 32 hours the eggs could not as a rule be fertilized at all. The experiment was then tried of adding to the sea-water, in which the unfertilized eggs were kept, small amounts of KCN in a graded series, and then examining the results of fertilizations undertaken after a stay of the unfertilized eggs of 75 hours in the solution. It will be noted that this period of 75 hours is more than three times the normal duration of life of the cell in normal sea-water. The results of this experiment are shown in summary form in Table 1.