26 . JOURNAL OF COMPARATIVE NEUROLOGY. 
GILson’s acetic-nitric-alcohol mixture and Carnoy’s acetic-chlor- 
oform-alcohol mixture were also used with advantage. Von 
LENHOSSEK (’95) who first investigated the centrosome in the 
spinal ganglion cells of the frog used an aqueous solution of 
corrosive sublimate. DEHLER (’95) stated that osmic prepara- 
tions give unsatisfactory results ; nevertheless Lewis (’96) has 
obtained very beautiful results from her osmic preparations of a 
certain annelid. HoLMGREN (’99) employed the fluid recom- 
mended by Carnoy. NELIs (’00), who studied mammalian nerve 
cells under pathological conditions for the purpose of demon- 
strating the centrosome, employed Gitson’s fluid. The present 
writer obtained satisfactory results from all these fluids but 
most frequently employed his own mixture, not because it is 
necessarily superior to the others, but because the writer was 
most familiar with its action. 
As staining agents, toluidin blue and thionin were used. 
The further procedure was the same as that given in the paper 
on the structure of the spinal ganglion cells.' 
Il. THE DIFFERENT CLASSES OF THE CELLS IN WHICH CENTRO- 
SOMES WERE DISCOVERED. 
Before going on to describe the structure of the centro- 
some, the different classes of the nerve cells in which the pres- 
ent writer has found the centrosome may be here enumerated. 
Two young white rats, having body weights of 4.6 and 6 
grams respectively, and three adult white rats, each having a 
body weight of approximately 150 grams were used. ‘The 
young rats were new-born. The regions examined from these 
animals were the cortex of the cerebrum, cerebellar cortex, 
corpus dentatum, motor cells in the ventral horn of the spinal 
cord and the spinal ganglia. The sections were cut 6 in thick- 
ness. Three or four slides were made from each of the regions 
just mentioned. Every section on each slide was carefully ex- 
amined. In this study it was observed that most of the nerve 
cells of young white rats possess a centrosome and a well 
1 loc. cit. 
