PREVENTIVE MEDICINE 211 



and like other disinfectants it acts quicker if the temperature is 

 raised to 65 F. It has a tanning effect on the skin, and is apt to 

 make leather, such as harness, brittle. 



The manner in which formaldehyde acts is not quite clear, but 

 it is known to modify the proteins, and owing to this action 

 objection is raised against its use for the preservation of milk and 

 other food, at any rate for children. Some believe, however, that 

 its action on the food proteins does very little harm. It is possible 

 that if ingested in fairly large doses carried over a considerable 

 length of time, it may have a tanning effect on the mucous lining of 

 the intestines. 



Formalin when in solution exposed to dry air undergoes poly- 

 merisation to form an inert substance, paraformaldehydc or 

 paraform (HCHO) 3 which may be reconverted to the gas formal- 

 dehyde by heat. Paraform tablets are used for aerial disinfection. 



Used as a liquid for disinfecting floors, stalls, and the like, it 

 should be applied not weaker than 5 per cent. By a 5 per cent, 

 solution is meant a 5 per cent, solution of the 40 per cent, 

 commercial formalin. As a liquid disinfectant it might with 

 advantage be more frequently used in veterinary practice. Accord- 

 ing to Muir and Ritchie, in the case of a pure culture a 5 per cent, 

 solution will destroy anthrax bacilli in a quarter of an hour and the 

 spores in five hours. For clothing infected with anthrax bacilli 

 " an exposure to the full strength of formalin for two hours is 

 necessary, and in the case of anthrax spores for twenty-four 

 hours." For the use of formaldehyde gas, see under Aerial 

 Disinfection. 



TAR (Fix Liquida, Wood Tar). Wood tar, also known as 

 Archangel or Stockholm tar, is a thick brown or brownish-black 

 bituminous fluid or semi-fluid obtained by the destructive distilla- 

 tion of wood, chiefly of Pinus sylvestris and other species of Pinus. 

 The gaseous products of the destructive distillation of wood are 

 carbon dioxide, carbon monoxide, and hydrogen with a little 

 methane. The aqueous portion (crude pyroligneous acid) usually 

 forms from 28 to 50 per cent, of the wood distilled and contains 

 acetic acid, methyl alcohol, allyl alcohol, and acetone as its chief 

 constituents, along with many other bodies in smaller proportions. 

 The tar itself is a complex mixture of various hydrocarbons, 

 phenols, and phenoloid bodies. By the distillation of crude tar are 

 obtained pyroligneous acid, oil of tar and a residue of pitch. 



Tar is a disinfectant and preservative, but it is not greatly 

 used in veterinary practice except for the purpose of disinfecting 

 and preserving the woodwork of stables, &c. Even for this 



