82 Proceedings of Royal Society of Edinburgh. [sess. 
point, would not care to insist upon it. I demur to the assertion 
that in the “ ripening ” of cheese we have an example of the direct 
conversion of proteid into fat, seeing that there is so much fat in 
cheese to begin with. What I believe happens is, that under 
bacterial fermentation the proteid (casein) is partly converted into 
caseoses or peptones, thus liberating much of the previously inter- 
stitially confined fat. 
IV. On the Antagonism between Potassium Salts and Calcium 
Salts in the Clotting of Milk. 
Ringer’s words are : “ The antagonism between calcium salts and 
sodium, potassium, and ammonium salts is limited to the preci- 
pitation of casein, and does not affect the chemical change from 
caseinogen to casein.” * In this research I did not investigate the 
action of the sodium and ammonium salts. It must be remem- 
bered that Dr Ringer used — 
(1) Milk diluted with water till it was 1 in 4 volumes. 
(2) Martindale’s preparation of rennet (reaction not stated), 
limeless, which did not clot the diluted milk. 
(3) Only one salt of potassium, the chloride ; at any rate, obser- 
vations with no others are published in the above paper. Ringer, 
in other words, alleges that the presence of a salt of potassium 
antagonises the precipitation of procasein by a calcic salt. I there- 
fore thought it well to study the general question of the effect upon 
the clotting of milk of as many potassium salts as I could lay my 
hands on, viz., twenty different salts. Believing, for reasons given 
already, that a neutral or faintly acid rennet will not bring about 
clotting in a solution containing such an amount of calcic salt as, 
with a more acid rennet, will cause clotting, I used a glycerine- 
extract of rennet of rather more distinctly acid reaction than 
Martindale’s. 
Half a test-tubeful of fresh neutral milk was dosed with 2 or 
3 c.c. of the solution of the potassium salt (30 per cent, solution), 
and then received 5 m. of the rennet ; the whole being thus heated 
to 50° C. 
A control experiment was in each case made, wherein the con- 
* Journal of Physiology, vol. xviii. p. 427 ; Nov. 16, 1895. 
