ON A FORMULA FOR DETERMINING THE WEIGHT OF THE 

 CENTRAL NERYOUS SYSTEM OF THE FROG FROM THE 

 WEIGHT AND LENGTH OF ITS ENTIRE BODY 



Henry H. Donaldson 



As THE living substance which constitutes the animal body becomes differen- 

 tiated into distinct tissues, the animal as a whole becomes more highly organized. 

 The fundamental tissues which are thus formed — namely, the epithelial, connective, 

 muscular, and nervous — are distinguished by the fact that each of them exhibits one 

 or more of the general characteristics of protoplasm developed to a greater or less 

 degree, whereas other of the characteristics are much less evident or apparently entirely 

 lacking. The combined activities of these differentiated tissues are exhibited in the 

 life-history of the entire animal. 



For the understanding of such an animal it is important to know the proportions 

 of the several tissues present in any instance, and whether we study the animal from 

 the standpoint of the number and size of the cell elements which constitute each 

 tissue, or from the more general standpoint of the weight of modified living substance 

 possessing the peculiar physiological characteristics of the tissue, the animal could be 

 described in terms of the analysis, that is, in quantitative terms of the several systems 

 of tissues which compose it. 



Thus, when tested in this way, animals like the dog, rabbit, and cat are found to 

 be dissimilar in their make-up, and a snake, for example, has a different tissue com- 

 position from a frog. To determine that these animals are thus differently constituted 

 is merely a first step, and is naturally followed by the attempt to determine whether 

 there are any laws governing the quantitative relations of these tissues either in the 

 animal series or in the same animal during its life-cycle. 



If it could be shown that one system varies in a definite relation to any or all the 

 others, we should have made a further step toward a comprehensive knowledge of the 

 animal examined ; and it is believed that the facts here to be presented constitute such 

 a step. 



The following paper describes the weight relations of the central nervous system 

 (brain and spinal cord combined) of the frog, to the tissues constituting the rest of 

 the body. The connection of this investigation with work already done along similar 

 lines can be stated very briefly. 



An attempt by Snell (1892) to correlate the increase in the weight of the encepha- 

 lon with some change in the remainder of the body led him to conclude that among 

 mammals and birds the weight of the encephalon increased in proportion to the area 

 of the body, when animals of different sizes, but otherwise similar, were compared. 



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