i74 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
The circumstances attending its development in cultures directly derived from 
the carcinomatous tumours will be given in detail in the following chapter ; although, 
as will be seen, in one of the cases A forms were also present in small numbers in 
the primary cultures obtained from the tumours, this small cell type, which I shall 
in future call type B, is the type to be associated with these primary cultures, and 
type A usually appears later as a result of the inoculation of type R into animals. 
I have said that I have isolated the small cell type under three different sets 
of circumstances : — 
r. From cultures of A in vitro. 
1. From animal lesions produced by the inoculation of A. 
3. Direct from the carcinomatous growths. 
The characters of the grDwth being similar under all these circumstances, the 
following description of type B is common : — 
3. The Morphology and Development of Type B 
Cultures examined microscopically in the fresh state show an organism for the 
most part spherical in form ; there are, however, present, especially in primary 
cultures from the growths, other shapes, i.e., oval and club-shaped forms. The size 
of the spherical forms varies from that of an extremely minute granule to an organism 
3/x to 4m in diameter. The cultures all show marked viscidity, and the 
organisms are seen microscopically in masses and clumps, with a large amount of 
intercellular material connecting them. When stained with methylene blue these 
masses have a very characteristic appearance ; the dark blue organisms stand out in 
a field of intercellular fibrillar material, which takes a reddish to red purple colour. 
The oval and club-shaped forms occur indiscriminately among the spherical forms in 
the clumps ; they are more marked in some than in other cases. If cultures of B 
procured from either of the abovementioned sources are studied in subcultures, it is 
seen that the average size of the organisms tends to become slightly smaller and more 
uniform, and the oval and club-shaped forms disappear. 
When inoculated into animals, type B usually undergoes important modifica- 
tion. Cultures which have not been carried through more than two or three 
subcultures in vitro are pathogenic to guinea-pigs and dogs, and produce in these 
definite lesions ; cultures which have passed through several generations lose patho- 
genic activity, and this loss of pathogenicity occurs especially early in the case of the 
cultures derived directly from the carcinomatous tumours. In rabbits 1 have not 
observed the development of any definite lesions after intraperitoneal inoculation of 
B, but when cultures are inoculated intravenously the organisms can be again recovered 
from the blood in a form which shows modification from the type injected. 
B has, therefore, been studied as recovered from the lesions produced in 
guinea-pigs and dogs, and from the blood of rabbits inoculated intravenously. The 
