98 



THE AMERICAN MONTHLY 



[May, 



Immunity Against Recurrence 

 OF Contagious Diseases. — Prof. 

 Tyndall has presented his views on 

 this subject, which, as they appear 

 to be of considerable interest, we re- 

 print from the Pall Mall Gazette: — 



' One of the most extraordinary and 

 vmaccountable experiences in medi- 

 cine was the immunity secured by a 

 single attack of a communicable dis- 

 ease against future attacks of the same 

 kind. Smallpox, typhoid, or scarla- 

 tina, for example, was found, as a 

 general rule, to occur only once in 

 the lifetime of the individual, the suc- 

 cessful passage through the disorder 

 apparently rendering the body invul- 

 nerable. Reasoning from analogy, I 

 have ventured to express the opinion 

 that the rarity of second attacks of 

 communicable diseases was due to 

 the removal from the system, by the 

 first parasitic crop, of some ingredi- 

 ent necessary to the growth and the 

 propagation of the parasite. 



' The cultivation of micro-organ- 

 isms, which is now everywhere car- 

 ried on, enables us to realize the 

 smallness of the changes which, in 

 many cases, suffice to convert a highly 

 nutritious liquid into one incapable of 

 supporting microscopic life. Various 

 important essays bearing upon this 

 subject have been recently published 

 in the Revue Scientifique. M. Bou- 

 ley there draws attention to the re- 

 sults obtained by M. Raulin in the 

 cultivation of a microscopic plant 

 named Aspergillus niger. The 

 omission of potash from Raulin's 

 liquid suffices to make the product 

 fall to one twenty-fifth of the amount 

 collected when potash is present. 

 The addition of an infinitesimal 

 amount of a substance inimical to the 

 life of a plant is attended with still 

 more striking results. For example, 

 one part in 1,600,000 of nitrate of 

 silver added to the liquid entirely 

 stops the growth of the plant. And 

 now we come to the important appli- 

 cation of this fact which has been in- 

 dicated by M. Duclaux. Supposing 

 the aspergillus to be a human para- 



site — living contagium — capable of 

 self-multiplication in the human 

 blood, and of so altering the consti- 

 tution of that liquid as to produce 

 death, then the introduction into the 

 blood of a man weighing sixty kilo- 

 grams of five milligrams of the nitrate 

 of silver would insure, if not the total 

 eftacement of this contagium, at all 

 events the neutralization of its power 

 to destroy life. The index finger 

 here points out to us the direction 

 which physiological experiment is 

 likely to take in the future. In an- 

 ticipation of the assaults of infectious 

 organisms, the experimenter will try 

 to introduce into the body substances 

 which, though small in amount, shall 

 so afiect the blood and tissues as to 

 render them unfit for the development 

 of the contagium. And subsequent 

 to the assault of the parasite he will 

 seek to introduce substances which 

 shall effectually stop its multiplica- 

 tion. There are the strongest grounds 

 for the hope that in the case of infec- 

 tious diseases generally such protect- 

 ive substance will be found.' 



The First Bacteria and their 

 Discoverer. — The^ Apotkeker- Zeit- 

 ung^ of New York, recently published 

 an interesting letter written by Dr. 

 Ferdinand Cohn, in which he says : 

 ' In the present time, when the times 

 of great men and great events are so 

 freely honored, it seems to me not 

 inappropriate to call to mind that two 

 centuries have passed since one of the 

 most important discoveries was made 

 in Holland. In a letter of the 14th 

 of September, 1683, from Delft, ad- 

 dressed to Francis Aston, Fellow of 

 the Royal Society, London, Antony 

 Van Leeuwenhoek stated that he had 

 discovered with his microscope living 

 animalcules w^ith most pleasing mo- 

 tion in the white matter adhering be- 

 tween his teeth.' These w^ere the first 

 bacteria that a human eye had seen. 

 Leeuwenhoek distinguished several 

 species, which he described and fig- 

 ured so correctly that they may be 

 still recognized without difficulty. 



