Mathilde L. Koch 269 



The fetal pig material was collected by my brother at the Chicago 

 Stock Yards. The fetuses selected were 50, 100, and 200 mm. in 

 length. The pregnant uterus was opened : and the fetuses removed. 

 The neck-rump length of each litter was taken and if the average 

 length corresponded to one of the three sizes mentioned above, 

 the entire litter was taken, placed upon ice and in this chilled 

 condition taken to the laboratory, where the brains were immedi- 

 ately removed, preserved and later analyzed according to the 

 same methods used for the rat material. 



RESULTS OF ANALYSES. 



The results from the chemical analysis of the brains from the 

 new born rat and the adult rat are given in table I: those of the 

 50, 100, and 200 mm. pig fetuses are recorded in table II, and 

 table III gives the summary of all the averages which have been 

 taken from the figures which were most consistent. The brain of 

 the 200 mm. pig fetus was plainly more differentiated, it is there- 

 fore left out of table III and of the final discussion of results. 



DISCUSSION OF CHEMICAL RESULTS. 



Before taking up a comparison of the new born rat with the 

 pig fetus it may be well to state, briefly, the chief chemical changes 

 in nervous tissue during growth. It is well known that the chemi- 

 cal composition of a tissue varies with age and that the water 

 content is one of the most important variables. Donaldson states 

 that, "the progressive diminution of the percentage of water in 

 the brain is a function of age and is not significantly modified by 

 any conditions to which the animals have been thus far experi- 

 mentally subjected." 5 He suggested that this "is to be regarded 

 as an index of fundamental chemical processes, which take place 

 in the more stable constituents of the nerve cells." 6 The principal 

 chemical differences due to growth, noted by my brother, are, "a 

 decrease in moisture,- proteins, extractives, and ash as the brain 

 increases with age, and an increase in cerebrosides, sulphatides, 



5 H. H. Donaldson : On the percentage of Water in the Brain and in the 

 Spinal Cord of the Albino Rat, Journ. of N enrol, and Psychol., xx, p. 143, 

 1910. 



6 Ibid. 



