58 DR DAV\''S OBSERVATIONS ON BLOOD AND MILK. 



One paii of serum and three parts of milk in mixture, coagulated at about 

 190", forming a soft tremulous mass, -which, by boiling, was rendered firmer. 

 Broken up and mixed with water and filtered, the fiuid had the properties of 

 weak AA'hey, and was not rendered turbid by acetic acid. 



A mixture of 1 part of serum and 4 of milk did not coagulate after several 

 minutes boiling ; but, keeping it on the fire, in about a quarter of an hour the 

 effect Avas produced. The coagulum formed was very soft. Mixed with water, 

 it rendered the water turbid at first ; but after a while, the finer particles subsid- 

 ing, left the water clear, and it was not affected by acetic acid. 



A mixture of 1 part of serum and 5 of milk, immersed in boiling water, at 

 least an hour, was found coagulated. The coagulum was of the consistence of 

 very soft custard. A like result was obtained, using a mixture of 1 of serum and 

 7 parts of milk. 



Lastly, a mixture of 1 part of serum and 10 of milk was liquid after more 

 than an hour's boiling ; but after about three hours' boiling, when a portion of 

 its water was expelled, it was found coagulated. 



As in these instances, the serum promotes the coagulation of the milk, so 

 also the latter may be considered as favouring the coagulation of the former ; 

 that is, viewing the milk as a diluent of the serum, having the effect of removing 

 fm'ther apart its albuminous particles, and comparing it as a diluent with water ; 

 two parts of which, I find, with one of serum, prevent the coagulation of the latter, 

 even at the boiling point, and thus heated, for many minutes. 



The property exhibited in the foregoing experiments is to be witnessed in 

 many other instances ; it may be, probably, in every instance in which liquid 

 casein and albumen are heated together in certain proportions. Mixtures of white 

 of egg and milk exhibit it even more strongly than serum and milk. With 

 equal parts of milk and white of egg, a firm coagulum is formed on boiling, the 

 fluid exuding from which is almost transparent, and is not sensibly affected either 

 by acetic acid or by the nitric acid. With 1 of white of egg and 5 of milk a 

 coagulum is formed of moderate consistence ; and Avith 1 of the former and 10 of 

 the latter a very soft coagulum, after immersion in boiling water for about a 

 quarter of an hour. I give these results, because, in no work on chemistry, with 

 which I am acquainted, have I met with any account of the effect of white of egg 

 on millc, even in culinary processes. Using the yolk of the ogg in place of the 

 white, the effect on milk has been, as might be expected, very similar ; the chief 

 difference in the coagulum being, that it has been somewhat softer. 



From similarity of composition, it might be inferred that the roe offish, mixed 

 and boiled with milk, Avould have the effect of coagulating it ; and this, I find, 

 is the case. The only other animal substance I have tried has been muscle ; it, 

 triturated and boiled with milk, did not coagulate it ; the muscular fibres, it may 

 be noticed, were found collected together in a mass in a singular manner. 



