Page:Popular Science Monthly Volume 69.djvu/22

From Wikisource
Jump to navigation Jump to search
This page has been proofread, but needs to be validated.

whereas in other cases half an egg will develop only into half an embryo. Investigators are still busy studying out these results, the final interpretation of which has as yet by no means been reached. The experiments have opened to us a new realm of inquiry full of astonishing surprises.

Experiments on artificial parthenogenesis have been much written about in the daily press, and many absurd things concerning this topic have been printed in the newspapers. Ordinarily the ovum requires to be fertilized in order to develop, but it has long been known that certain ova, of bees, of plant lice, of some Crustacea and of other animals will develop without being fertilized. To this process the term parthenogenesis has been applied. Artificial parthenogenesis designates the development of unfertilized ova which normally would not develop at all and which are stimulated to development by placing them under artificial chemical conditions. Doubtless many of you have seen in the newspapers these experiments referred to as if they gave the actual creation of life. Of course that is nonsense. The life is there in the ovum. What artificial parthenogenesis accomplishes is to supply a stimulus, chemical in nature and capable of replacing the fertilization by the spermatozoon, which would otherwise be necessary. The possibility of artificial parthenogenesis was first partially demonstrated by Richard Hertwig, but has been perhaps more studied by Professor Loeb, now at the University of California, than by any one else. Hertwig produced artificially only a development of very limited degree, but Loeb by treating the eggs of a sea-urchin for about two hours with a weak solution of magnesium chloride succeeded in 1899 in producing larval sea-urchins (so-called plutei) from unfertilized ova. He concludes from this that fertilization is a chemical process, and that it is distinct and separate from hereditary transmission. No words of mine are needed to emphasize the importance of such investigations, for they are basic.

A line of work combining experimental and observational methods in which I have been especially interested deals with the problem of growth. It can be shown statistically that the growth of the embryo in early stages goes on at an enormous rate, and also that during the period of fœtal development that rate is constantly declining, so that something over 98 per cent, of the growth power is lost by the time of birth. After birth decline in the growth power continues, but gradually the decline becomes slower and slower, so that though growth is slight in rate, the growth power is long continued. A study of the condition of cells while this decline of the growth power is going on reveals to us that while the growth power is rapid the nucleus of the cell is active and well developed, and that the protoplasm of the cell is but slightly developed. As the proportion of protoplasm in the cells increases the power of growth diminishes, and as differentiation