The Theories of Cell Development. 
121 
Nevertheless I am not prepared to deny that transformations of 
the true gland tissue of the parts involved, play a certain role in 
producing the texture of cancerous growths. But just how far they 
are atrophied and perish, how far at times a formative activity may 
lead to their transformation, are matters as to which it is difficult 
at present to form a judgment, and to which I hope to return at 
some future time. 
Meanwhile I cannot avoid calling attention to two more of 
Billroth’s woodcuts — fig. 148, page 648, and fig. 150, page 651 
( Joe . cit.) — the first representing the “ extension of cancerous tumour 
into the fatty tissue about a lymphatic gland,” the second “ cellular 
infiltration of the fatty tissue in the periphery of a hard cancer of 
the breast.” Either figure might have been drawn from the altered 
fat in the sections of the two breasts described in this paper, and the 
appearances are such that, as Billroth well remarks, “ we can 
scarcely avoid thinking that in these cases also, white blood-cells 
escaping from the vessels cause the cellular infiltration.” With 
this suggestion I heartily agree ; but the real and difficult point in 
the analysis of cancerous tumours, as of so many pathological trans- 
formations, is to define with precision the exact part which the 
emigration of white blood-cells plays in the process, how far it 
is the principal, how far merely the accessory alteration. This 
report is offered as a preliminary contribution to the study of this 
question, now become so important in reforming our pathological 
doctrines. 
I may mention, in conclusion, that the microscopical sections 
referred to were all made by Dr. E. M. Schaeffer, and that they 
are permanently preserved in the Microscopical Section of the 
Museum, where they may be examined by anyone interested in the 
subject. — Deport to the Surgeon- General of the United States’ 
Army. 
Army Medical Museum, Microscopical Museum, 
April 29 th , 1872. 
VII. — The Theories of Cell Development. By I. N. Danforth, 
M.D., Pathologist to St. Luke’s Hospital, Chicago, U.S.A. 
• 
From a very early period in the history of medicine the idea pre- 
vailed that there must be some anatomical unit, some elementary 
part or particle, which, whatever might be its form or size, must be 
regarded as the true seat and home of vitality. Without the aid of 
