8EKUM THERAPY 743 



^ They are put in an incubator for several days to prove 

 their sterility; if the serum turns cloudy it is rejected. 

 Most serums will keep a year if preserved with a slight 

 amount of carbolic acid or if treated by repeated steriliza- 

 tion below 100° C. Cloudiness in a serum indicates that it 

 is unfit for use. 



The activity of a serum is estimated in two ways. First, 

 the amount of antitoxic serum required to neutralize a 

 given volume of toxin of known strength. Second, the 

 strength is stated in units. Thus a test toxin is prepared, 

 ^^ cc. of which constitutes the smallest fatal dose of a 

 guinea pig. This amount of toxin is neutralized by ^Vb" o^ 

 a tinit of antitoxin. Or, to put it another way, 1 unit of 

 antitoxin will protect 1,000 guinea pigs against the small- 

 est fatal dose of toxin. 



The dosage is, then, reckoned in units of antitoxin, 

 which is the most accurate method. While this modei of 

 standardization is applied to the use of diphtheria antitoxin, 

 unfortunately it is not employed in the case of the other 

 serums where the dose is given in cc. This is inadvisable, 

 as different manufactures possess different antitoxic 

 strengths. 



The toxin of tetanus is developed by the bacteria of 

 this disease, which gain entrance through wounds of the 

 tissues of the body. The bacilli of tetanus are not distrib- 

 uted by the blood, but remain at the site of infection, and 

 the toxins they produce are taken up by the peripheral 

 nerve endings in the vicinity and carried along the axis cyl- 

 inders of the motor nerves to the central nervous system. 

 The same thing happens in rabies. When the toxins reach 

 the spinal cord the symptoms of tetanus appear and finally 

 death occurs, when the important centers of the medulla 

 become intoxicated. Tetanus bacilli live in the soil, and 

 wounds which are contaminated with dirt or foreign bodies, 

 and those which do not have free access to air— as bruised 

 or punctured wounds — are chiefly liable to the development 

 of tetanus. It will thus be seen that tetanus does not 



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