Page:Popular Science Monthly Volume 71.djvu/378

372 and we should hardly anticipate that its increase would have a deleterious effect. But such is, it seems to me, clearly the case. But it is not merely, of course, a question of the increase of protoplasm which we must bear in mind in estimating the cause and effect, but also the question of differentiation, in consequence of which protoplasm becomes something else and different from what it was before. This alteration, then, together with the increase of the protoplasm, is the change which in all parts of the body marks the passage from youth to old age.

It seems to me not going at all too far to say that the increase of protoplasm is a fundamental phenomenon. I wish to give you a more precise notion of this increase; and I am glad to be able to do so in consequence of a research carried on by Professor Eycleshymer in my laboratory and completed by him afterwards in his own laboratory at the University of St. Louis. He studied the development of the muscle fibers in the great salamander, known scientifically by the name of Necturus. These muscle fibers are somewhat cylindrical in shape. Their ends can be accurately determined so that the precise length of a fiber can be measured, and its diameter also. Hence the total volume of a fiber may be calculated. It is possible also to measure the nuclei and to count the number of nuclei in a fiber. Thus by measuring the diameter and length of the fiber, and then estimating the number and the diameters of the nuclei, we can calculate the proportions. As a matter of fact, the nuclei remain nearly constant in volume, not really quite so, but sufficiently constant to serve as a basis of measurement. Dr. Eycleshymer found that when a Necturus had a length of eight millimeters, it possessed, for each nucleus in its muscle fiber, 2,737 units of protoplasm, but when it was seventeen millimeters, it possessed for each nucleus 4,318 units per nucleus; at twenty-six millimeters, 8,473 units; and in the adult, which measures approximately 230 millimeters, it has 22,379 units per nucleus. In other words, as a salamander passes from the eight-millimeter condition, when the development of its muscle fibers is just fairly begun, up to the adult state, when the differentiation of the muscle fibers has been completed, it increases the proportion of protoplasmic substance and protoplasmic derivatives from 2,700 to 22,300 per nucleus. I give round numbers. The increase is approximately sevenfold. There is in the adult in the muscle fiber seven times as much protoplasmic substance in proportion to the nucleus as there was at the start of development when the muscle fiber could first be clearly recognized as such. This is an accurate measure and gives us a good idea of the general law of protoplasmic increase. It is the only instance, I yet know of, in which we have an accurate measure and can give quantitative values, though we do know that there is a more or less similar increase occurring in perhaps every tissue of the body.