of Edinburgh, Session 1885-86. 
615 
With regard to the colonies in solid media, the first appearance is 
white, even when the growth is of some size. The change of colour 
takes place gradually, and it remains yellow. Spore formation, as 
shown by the bright orange colour, is seldom seen in solid media. 
I am unable to explain this, except that the environment is unfavour- 
able to the production of spores, while it is favourable to the 
ordinary vegetative growth. Then, when secondary cultivations 
were made, the same colour was only once reproduced. If change 
occurred, it was in the direction of more distinctness in the colour, 
apparently showing that the change of medium was more favourable 
for spore production. It would be interesting to know whether 
coloured growths of vaccine lymph are alkaline or acid in reaction. 
If the orange growth is composed of spores, it should correspond to 
the alkaline clear lymph. At the same time, the white and yellow 
should show an acid reaction similar to that given by opaque lymph. 
We may suppose the yellow colour to be produced by a mixture of 
vegetative and spore growth, i.e., white and orange. 
3. Microscopic Appearances of the Organisms . — My observations 
show that the size of the organisms increases with the age of the 
cultivations. Incubation has also some effect, and one medium may 
be more suitable than another for its growth. Thus in Koch’s jelly 
the micrococci were smaller than those in agar after incubation. As 
the material was the same, this could only be explained by more 
rapid growth. Thus we find that the same organism derived from 
the same source, presents different appearances according to the 
environment and other favourable circumstances. It does not follow, 
however, that the same forms will produce the same effects. Nor 
does it follow that different-sized organisms will not produce similar 
physiological effects. The truth seems to be that the larger 
organism is the more powerful. The embryonic form is milder in 
action. 
4. Physiological Action . — The results of experiments, although 
few in number, appear to show that the embryonic form is milder 
in action than the more mature form of organism. Thus clear 
vaccine lymph and orange vaccine, both containing minute organisms, 
produced only a local result. Opaque variolous lymph and white 
and yellow vaccine cultivations and white variolous cultivations, 
containing larger organisms not found in clear lymph, produce an 
