386 
It is doubtful, however, whether the method ever found any very 
extensive application. According to Leach (17) salicylic and benzoic 
acids are now rarely used as milk preservatives. Salicylic acid 
in quantities sufficient to preserve affects the taste of the milk. Rich- 
mond (18) found a new food preservative to consist of acid potas- 
sium fluoride, KHF 2 . 
As a general thing these substances are employed only in small 
amounts, and at present there is considerable difference of opinion 
as to what effect these various substances in the small amounts usu- 
ally present in milk and other foodstuffs exert upon the human system. 
Thus, according to Trillat (19). formaldehyde renders the casein of 
milk more or less indigestible, and a further objection to its use is 
that part of it remains unaltered in the various foodstuffs with which 
it is admixed, and being absorbed as such by the system may act 
injuriously on the digestion. On the other hand, Rideal and Foul- 
erton (20) have observed that formaldehyde at a dilution of 1 : 50,000 
or 0.05 per cent of boric acid and borax will preserve milk twenty- 
four hours, and that these amounts of these substances have no 
effect on the peptic and pancreatic enzymes, while this quantity of 
boric acid greatly retards the diastatic power of saliva, the formal- 
dehyde having much less effect. Experiments with kittens, rabbits, 
and guinea pigs proved, according to these observers, that the 
amount of formaldehyde required to preserve milk has no effect on 
their proteid metabolism. Fish were not affected in six days in water 
containing 1 part of formaldehyde in 50,000 parts of water, and 
frogs stood a concentration of 1 : 20,000 without injury for two hours. 
The conclusion drawn by these writers from their investigation is 
that the quantities of these substances necessary to preserve milk 
twenty-four hours have no appreciable effect on the digestibility of 
the milk, and that in these quantities formic aldehyde and boric acid 
interfere less with the pancreatic digestion of casein than tea, claret, 
and Worcester sauce. Formaldehyde, 1:50,000, does not appear to 
have any injurious action upon animal tissues, or on nutrition. On 
the other hand, Otto Hehner (21) has criticized the experiments by 
Rideal and Foulerton on the ground that they were not properly con- 
trolled, and this author seems inclined to believe from the results 
obtained that these substances, in the quantities employed, were in 
reality injurious to the animal organism. T. M. Price (22), working- 
in the Biochemic Division of the Bureau of Animal Industry, U. S. 
Department of Agriculture, has made a valuable contribution to this 
subject. He has studied the effect of some food preservatives on the 
action of the digestive enzymes, especially the effect of formaldehyde 
on the preservation of milk and the effect of this substance on the 
digestibility of the milk by the digestive enzymes in vitro and in the 
