GROWTH-CHANGES IN MAMMARY APPARATUS OF DASYURUS. 207 
both the cytoplasm and the nucleoplasm of the cells is set 
free into the alveoli. 
In the same year Arnold (2) pointed out that the parts of 
the cells which lie in the lumen may be artifacts or may be 
produced by the energetic sucking of the young causing a 
lesion of the cell walls. Finally, Bertkau (6), in 1907, carried 
out a series of investigations on suitable fixing and embedding 
methods, and, from very careful comparisons of the results 
obtained by various processes, came to the following con- 
clusions on this subject : (1) The appearances described as cell 
decapitation and the expulsion of nucleoplasm are artifacts 
due to unsuitable hardening or embedding or to post-mortem 
chauges in the material itself. (2) Suitable methods show the 
epithelium of the alveoli to be essentially similar to that in other 
glands. (3) The production of milk is a purely secretory occur- 
rence in no way connected with the necrobiosis, either partial 
or complete, of the epithelial cells. Finally, it is to be remem- 
bered, as Lane-Clay pon and Starliug (loc. cit.) pointed out, 
there is no evidence to show that the disintegration of the 
gland-cells would give rise to the specific constituents of 
milk. 
As a result of my investigations on Dasvurus, the domestic 
cat, the rabbit, and the guinea-pig, the glands of which were 
fixed immediately after death, I find mvself in entire aofree- 
ment with the conclusions of Bertkau stated above. I find that 
Zenker’s fluid or picro-nitro-acetic acid is not a satisfactory 
fixative for the mammary gland, and that picro-corrosive-acetic 
acid or potassium bichromate and acetic acid gives very good 
results. Particular care was taken that the changes from one 
fluid to another during staining and embedding should not be 
too sudden. The sections studied were about 5/ithickand the 
results in the various animals very similar. Where the tissues 
are not well fixed, and in the places where the knife had a bad 
edge, the lumena of the alveoli contain pieces of torn cells sug- 
gesting that decapitation had occurred. Sometimes also nuclei 
are present in these places, but it is clear from the condition of 
the surrounding tissue that the section is suffering from faulty 
