DISEASES OF CATTLE 39 



somewhat more danger from fire when this method is employed 

 than in those previously described. Not less than 25 ounces of wood 

 alcohol should be employed for disinfecting 1,000 cubic feet of 

 space. 



The advantages of formaldehyde may be summarized as fol- 

 lows: (1) It is one of the most powerful germicides known. (2) Its 

 action is not interfered with by albuminous sujbstances. (3) It is 

 not poisonous and may therefore be used for disinfecting hay and 

 grain without destroying these for food purposes. (4) It is not in- 

 jurious to delicate fabrics, paint, or metals. (Formalin solutions 

 will attack iron, but not other metals). 



The disadvantages are, briefly, as below: (1) The gas has a 

 strong tendency to condense in cold weather and is not reliable as a 

 disinfectant when the air temperature is beloAV 50 F. (2) It is 

 necessary to seal tightly, all compartments which are to be disin- 

 fected with the gas in order that penetration may be secured and 

 that the required concentration may be maintained for a sufficient 

 length of time. 



Carbolic Acid (Phenol). Pure carbolic acid is solid at ordin- 

 ary temperatures and crystallizes in long white needles. It may be 

 Eurchased in this form or as liquefied carbolic acid (Phenol lique- 

 ictum, U. S. P.). The latter form is prepared by adding 1 part of 

 water to 9 parts of the crystals and is employed by pharmacists on 

 account of convenience in dispensing. Carbolic acid must not be 

 confused with "crude carbolic acid" and "liquid carbolic acid," 

 which are described below. 



For disinfecting purposes carbolic acid is generally used in 

 watery solution, though powder containing it are sold. A 5 per 

 cent solution of crystallized carbolic acid in water is recommended 

 for general use, for, although weaker solutions have been found ef- 

 ficient for destroying many nonspore-bearing bacteria, the condi- 

 tions found in practice vary widely and in some cases hinder the 

 action of the disinfectant. As carbolic acid dissolves slowly, the 5 

 per cent solution should be prepared with warm water, using care 

 to see that all is dissolved before use. For disinfecting large sur- 

 faces a spray may be used and the disinfectant should be applied 

 liberally. Garments or implements to ibe disinfected should remain 

 in the 5 per cent solution for at least one hour. 



The advantages of carbolic acid are: (1) It is reasonably ef- 

 fective for destroying nonspore-bearing bacteria. (2) its action is 

 only slightly interfered with by albuminous substances. (3) It does 

 not destroy metals or fabrics in a 5 per cent solution. (4) It is read- 

 ily available at all pharmacies. 



The following disadvantages may be mentioned: (1) It can 

 not be depended upon to destroy the spores of such bacteria as an- 

 thrax and malignant edema. (2) It is expensive (the pure phenol 

 costs approximately 75 cents per pound). 



CRUDE CARBOLIC ACID. 



Probably no substance is so widely used in this country as a 

 household and farm disinfectant as crude carbolic acid, and at the 



