SERUM THERAPY 545 



menced, doses first of 10, then of 15 and 20 c.c. being given every 2 or 3 days. At 

 the end of 6 weeks increasing doses of 50, 100, 150 c.c. can be inoculated into the 

 jugular vein. After these enormous doses intra-venously the horse may suffer 

 from temporary disturbances of health such as sweating, colic, diarrhoea and rise 

 of temperature (1 or 2 C.). Immunization is complete in about 3 months. 



The blood may be collected for therapeutic purposes 10 days after the last 

 inoculation. 



(iii) Behring advises inoculating the horse in the first instance with a 

 mixture of toxin and antitoxin prepared in such a way that its inoculation 

 into small animals leads to a slight illness. The treatment is subsequently 

 continued by inoculating pure toxin. This method is based upon that 

 described for the preparation of diphtheria antitoxin (p. 265). 



(iv) Vaillard immunized a rabbit by injecting it sub-cutaneously on several 

 occasions with very small doses of the spores of tetanus free from toxin but 

 mixed with a little lactic acid. An animal treated in this way resists the 

 inoculation of ordinarily lethal doses of tetanus toxin but its blood shows no 

 appreciable antitoxic property. 



4. Serum therapy. 



The antitoxic properties of the blood of animals immunized against tetanus 

 were demonstrated by Behring and Kitasato. 



The blood of an immunized rabbit is capable of neutralizing tetanus toxin. 

 This property is present in serum free from all cellular elements and is demon- 

 strable both in vivo and in vitro. It is not found in the blood of non- 

 immunized animals. 



The blood of naturally immune animals, such as the fowl, possesses no anti- 

 toxic property though it easily acquires the property if the animal be inoculated 

 with tetanus toxin. After two or three inoculations of 20 c.c. each into the peri- 

 toneum of a fowl the blood of the animal exhibits, after the lapse of 1220 days, 

 powerful antitoxic properties. Similarly, the blood of rabbits immunized by the 

 inoculation of small doses of spores does not possess antitoxic properties but these 

 properties may be conferred by inoculating the animal with tetanus toxin. 



The milk of immunized animals is also actively antitoxic. The white of 

 egg of fowls which have been treated with toxin is not antitoxic. 



Preparation of tetanus antitoxin. For the practical application of serum 

 therapy to man and animals the serum of the horse is used. For laboratory 

 work, rabbits are a good source of antitoxic serum. 



Horses are immunized in the manner described above. 1 



After 3 months the serum of the horse is ready for use. The antitoxic 

 property is maintained and even increased by inoculating large doses of 

 toxin into the jugular vein or beneath the skin of the animal at intervals. 

 After each inoculation the antitoxic strength of the serum is lowered for the 

 time being ; the horse therefore must not be bled until 12 days have elapsed. 



The serum preserves its properties when dried in vacuo. In this way, a 

 very powerful serum may be kept indefinitely and in small bulk. 



Standardization of the antitoxin. In determining the antitoxic content 

 of a serum the notation of Roux and Behring is used, which calculates the 

 content according to the volume of serum required to immunize 1 gram 

 weight of mouse. A serum is said to be active in 10 QQQ 000 if O'l c.c. of the 

 serum is sufficient to immunize 100 kg. of mice or when a mouse weighing 

 20 grams is rendered immune by the inoculation of 0'000,002 c.c. of serum. 



In vitro the antitoxic content of the serum is measured by the quantity 



1 For full details of technique, reference should be made to the section on immunization 

 against diphtheria. 



2M 



