'i Weight of the Central Nervous System of the Frog 



DuBois (1898) took up this conclusion of Snell and elaborated it (for mammals 

 alone), making a more careful analysis of the conditions underlying the calculation, 

 and finally giving a formula for the relative weight of the encephalon in mammals, 

 which is very satisfactory, and which differs but slightly from the formula given by Snell. 



The study of the work of Snell and DuBois led me to attempt the extension of 

 their results. Their formulae apply to the relative weights of the encephala in mature 

 mammals, so that, in order to get the absolute value, the weight of one of the pair of 

 encephala must be known. They do not discuss the increase of the encephalon in 

 weight in the same mammal during its growing period, nor do they extend their 

 observations to other classes of vertebrates or to the entire central nervous system. 

 In the present instance we have sought to determine whether we could obtain a 

 formula which would express the weight of the entire central nervous system at any 

 time during the growing period of an animal, and in this instance have chosen the 

 frog. For the study of this problem there were available in the laboratory records on 

 two species of frogs, the bullfrog and leopard frog. It may be noted in passing that 

 for a study of this kind the frog presents certain advantageous peculiarities, as it 

 exhibits only a comparatively slight alteration in the bodily proportions during growth. 



Like other vertebrates, its increase in length is most rapid during the earlier 

 portion of the growing period, and later, the increase in length becoming slow, the 

 body enlarges at right angles to its long axis, and the animal becomes thicker. 



Nevertheless, the weight relations between the muscles of the legs and the 

 remainder of the body remain nearly constant (Donaldson, 1898; Donaldson and 

 Schoemaker, 1900), and in this respect the frog shows but very slight changes in 

 proportion. 



In the foregoing characters the two species which have been examined, the bull- 

 frog [Rana catesbiana) and the leopard frog [Rana virescens), were nearly alike. 

 For each species the series of observations was extensive, comprising data on the 

 body weight and length, and also on the weight and length of the brain and spinal 

 cord, together with other measurements not needed for this investigation (Donaldson, 

 1898; Donaldson and Schoemaker, 1900). 



On looking at the curve previously published, for the weights of the brain and 

 spinal cord arranged according to the body-weight (Donaldson and Schoemaker, 1900, 

 p. 117), it appeared that the weights for the central nervous system (brain and spinal 

 cord combined) were so related as to suggest a logarithmic curve, and this suggestion 

 was at once tested.' 



The trial was made by forming a curve depending on the logarithms of the body- 



1 In a paper entitled " Zur Anthropologie des Riicken- the body-weights of the dogs examined, and find that it 



markes" (Coi-resp.-Bl. d. deutsch. Anthrop. Gesellsch., No. gives a much flatter curve than that based on the weights 



10,1895), Ranke presents observations on the weight of the of the spinal cords. In this instance, therefore, a logarith- 



spinal cord in dogs of different body-weights. He suggests mic relationship between the nervous system (spinal cord) 



that the curve which illustrates his Tabelle 3 has the form and the rest of the body does not appear, but, so far as I am 



of a logarithmic curve, but does not test the suggestion. aware, this is the first record of the suggestion that such a 



I have determined the curve formed by the logarithms of relationship might exist. 



18 



