CHEMICAL PREPARATIONS AND DRUGS. 113 
do so in a much feebler degree than human beings, and in a manner different from 
the latter. Animals whose organisms respond to the toxin only very rarely show such 
symptoms as irritation of the mucous membranes; the chief symptoms in their case 
being local swellings at the place of injection, attended by a considerable rise in 
temperature and distaste for food. When these symptoms disappear within a few days, 
the inoculation is repeated with about 1'/2 times the previous dose of toxin. By this 
method it was found possible in many cases of horses, after an initial dose of */2 g. 
of rye-pollen, to increase the dose to extracts up to 50g. of pollen. Gradually anta- 
gonising substances against the pollen-toxin were formed within the blood-serum of 
the animals, as was demonstrated for one thing by their slow habituation to the 
poison. Another method of proving the formation of the gradual antibodies was the 
fact that a drop of active toxic solution, mixed with a little of the blood-serum of 
animals which had undergone a prolonged course of inoculation, failed to provoke 
the usual irritation of the mucous membrane sensitive to hay-fever, whereas the same 
toxin-solution after being mixed with the normal serum of various species of animals 
underwent no decrease of activity. It was even possible, within certain limits, to 
follow quantitatively the neutralisation of the toxic action on eyes sensitive to hay- 
fever, and on the basis of a constant dose of the toxin-solution, to measure the degree 
of activity of the serum, its so-called valency, within about 10 p.c. of accuracy. This 
was done by incorporating into the eye of the patient one drop of a toxin-solution 
of 1:20000 after mixing it with an equal drop of the serum under examination. If no 
symptoms of irritation were observed, the toxin was completely neutralised by the 
protective substances of the serum. When the serum is diluted twice, five times, 
m-times, and a mixture of the same toxin-solution and of the diluted serum is intro- 
duced into the other eye of the patient after a lapse of about 10 minutes (it is quite 
possible to examine both eyes alternately at intervals of 10 minutes), adegree of 
dilution is finally observed in which the poisonous action of the toxin is no longer 
suspended, but in which it finds expression in a more or less pronounced irritation. 
By suitably varying the degree of dilution, a point is reached where only subjective 
irritation, such as burning or itching, is manifested, but where no objective symptoms 
are observed. This point is called the limit of reaction, and the degree of dilution 
of the serum which, together with the toxin solution, sets up this limit of reaction, 
is known as the degree of activity, or more briefly the valency, of the serum. It is 
worthy of note that, in the author’s own experience, after experiments of this character, 
repeated several thousand times, neither local immunity nor local hyper-sensitiveness 
of the conjunctiva was observed, and also that the minimum limit of the quantity of 
toxin which provoked any effect whatever in him was not materially increased. However 
simple this test by means of the ophthalmo-reaction*’) may appear to be, it has never- 
theless this drawback that it is not easy to find persons who are suitable subjects for 
such experiments. Attempts have therefore been made to utilise the reaction employed 
for differentiating other vegetable species of albumin for the estimation of the value of 
the protective serum. So far, however, these experiments have not been successful; 
neither old nor fresh pollens or their extracts have ever yet afforded such a reaction. 
Dunbar discovered, nevertheless, that in the case of a small number of hay-fever 
patients the blood-serum had a clear, albeit faint precipitating action upon pollen 
*) The ophthalmo-reaction can be very easily applied for the diagnosis of hay-fever as distinguished ~ 
from other similar affections which are not due to infection by pollen (e. g. Coryza nervosa) by means of our 
Hay-Fever Diagnostic, which is supplied free of charge and ready for use to the medical profession. 
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