INFLUENCE OF THE SENSE-ORGANS ON THE LOSS IN WEIGHT DURING STARVATION.
The influence of the sense-organs on the rate of regeneration is so clearly marked when muscular activity is excluded as the determining factor that it seemed apparent that other metabolic activities might be used as a measure of this influence.
Mayer (1914) has shown that when Cassiopea is starved in sea water from which all food material has been removed by either careful filtration or by heating to 71° C. and restoring by distilled water the amount lost by evaporation, the loss of weight follows a course which can be expressed mathematically by the formula y =w(1 — a)z, in which y = the weight on any given day, w the original weight, z the number of days' starvation, and a constant, " the coefficient of negative metabolism." The greater part of the loss in weight appears to be borne by the mesogkea, since this tissue constitutes by far the greater bulk of the body, as is shown by histological examination of the tissues and chemical analysis of medusie before and after starvation. The simple character of the law which governs the loss of weight in Cassiopea during starvation also indicates that substances of the same sort serve to maintain the medusa throughout nearly the entire course of starvation. As the result of starvation the cells become reduced in size, some degenerate and disappear, while at the same time the mesogkea becomes highly vacuolated. Within the short period of time covered by these experiments very little histological change could be recognized in the cells. The change in the appearance of the mesoglcea was, however, much more marked in that vacuolization had become more easily noticeable.
There is clearly a different tissue chiefly involved in the loss of weight during starvation and in regeneration (see page 131), so that these experiments present a standard of measurement of metabolic activity sharply distinguished from that employed in the study of regeneration.
Mayer (op. cit.) has pointed out that the value of a (the coefficient of negative metabolism) has a different value for practically every set of experimental conditions. Thus this value differs when employing entire medusze, regenerating portions of oral arms or the bell-margin, disks from which arms and stomach had been removed, or half-disks. Besides,
on account of the relative activity of the zooxanthelhe (symbiotic algae), the rate of starvation differed greatly when the experiments were carried on in the diffuse light of the laboratory or in darkness.
In these experiments, where the disks were prepared by one of the three types of operations previously described, there was no necessity for taking precautions to remove the normal food materials from the water. Water from the regular laboratory supply pumped through vulcanite pipes by a vulcanite pump was regularly used, as no difference was found when water brought in glass jars from the ocean was used.
Mayer has called attention to the fact that regenerating specimens, during the first days of any experiment, starve more rapidly than normal medusie.
In the same manner during the first half day of any experiment the member of any pair of half disks which showed the highest metabolic activity showed also the greatest loss in weight, yet even in the course of these experiments the difference in rate became less marked toward the end of the period of observation. This appears most clearly in experiments in which active and inactive specimens are compared (fig. 10), while the nearest approach to actual convergence is shown in the series in which activated and inactive specimens are compared (fig. 1).
The previous researches on inanition in invertebrates have dealt with either the chemical or histological changes brought about by the disturbances in normal metabolism caused by this condition, and need not be reviewed in this connection. In general, it has been observed that there is a shrinkage in size and frequent degeneration of the cells of all parts of the body. The epithelial tissues in general have a tend ency to lose their cell-wall and to become a syncytium. Usually the loss of material is not nearly so selective as in the vertebrates; practi cally all organs become involved in the loss in an early stage of inanition, except in forms in which there is some special storage tissue, as the fat bodies of insects.