*4 



NATURE 



[May 4, 1882 



afterwards becoming opac and degenerating into a yel- 

 lowish-looking dt'bris, and hereby implicating and destroy- 

 ing the organs in which they are located] — has been 

 shown to be an infectious malady communicable from 

 one human being to another, from man to animal, and 

 from animal to animal. 



The successful experiments of inoculating with, feeding 

 on, and causing to inhale human tubercular matter, carried 

 out on the lower ani mals, such as guinea-pigs, rabbits, dogs, 

 pigs, &c, by Villemin, Dr. Wilson Fox, Mr. John Simon, 

 and Dr. Burdon Sanderson, but especially by Cohnheim 

 and Salomonsen, Tappeiner, and Baumgarten are con- 

 clusive in these respects. Similarly it has been shown 

 that the tuberculosis of cattle or Perlsucht is communi- 

 cable not only within the species but also to other animals. 

 Whether Perlsucht is also communicable to man, espe- 

 cially through meat and milk, as is maintained by some 

 observers (Semmer, Baumgarten, and others), is as yet 

 an open question, and, as must be obvious to every one, 

 one to which fearful importance is attached, considering 

 how great the distribution of this disease is in the bovine 

 species. What the cause of the malady is, has until now 

 been undetermined, although it has been at various times 

 surmised that, like other infectious diseases, it is of a 

 parasitic origin. Thus Schiiller, and especially Klebs, 

 have tried to prove that owing to the presence of micro- 

 cocci in the tubercular deposits, these micrococci were 

 the materies morbi. And indeed Klebs maintains to 

 have succeeded in cultivating outside the body of an 

 animal, i.e. artificially the "monas tuberculosum," as he 

 calls the said micrococcus, and to have again produced 

 the tubercular disease by inoculating animals with this 

 purified micrococcus. Klsbs' observations and conclu- 

 sions have not been accepted as reliable, and it has been 

 reserved for Dr. Koch to discover the real cause of the 

 disease, in identifying it with a specific bacillus. In a 

 weighty paper, " The Etiology of Tuberculosis," published 

 in the Berlin Klin. Wochenschr, 1882, No. 15, Dr. Koch 

 sets forth the whole course of his investigation, the 

 methods and experiments, all his observations and definite 

 conclusions on this question, and anyone who peruses 

 carefully this paper will come to the conclusion that 

 Koch's results are to be accepted with unconditional 

 faith, and I have no manner of doubt will be considered 

 by all pathologists as of the very highest importance. 

 To those who are familiar with Dr. Koch's previous work, 

 especially that on the etiology of splenic fever or Anthrax, 

 and his observations on pathogenic Bacteria, this last 

 work of his, on the Etiology of Tuberculosis, will be an 

 additional and brilliant testimony to his ingenious and 

 successful method of research. 



The first step in the inquiry was to ascertain whether 

 any definite form of microphyte is constantly present in 

 the tubercular deposits. This question could not be 

 solved by the ordinary methods of research, but with new 

 methods ; it was decided in the affirmative. For the 

 demonstration of the presence of the specific bacillus — 

 which Koch calls the tubercle-bacillus — the following 

 method proved successful : Tubercular deposit fresh, or 

 after hardening with reagents, is stained for twenty to 

 twenty-four hours— at a temperature rf 40 Centigrades, 

 only half to one hour is required — with a half per cent, 

 solution of methylene blue, to which a small quantity of 

 a 10 per cent, solution of caustic potash is added. After 

 this, the tubercular material is stained for a minute or 

 two in a concentrated watery solution of vesuvin. and then 

 washed in distilled water. When examined under the 

 microscope, all elements of the tubercular deposit, such 

 as cells, nuclei, fibres, and granules, appear of a brownish 

 colour, while the tubercle-bacilli alone stand out very 

 conspicuously in a beautiful blue tint. 



By this method Koch ascertained the constant presence 

 of the specific bacillus in the tubercular eruption in man 

 and animals, including the Perlsucht of cattle, both in 



spontaneous tuberculosis, as well as artificially produced, 

 i.e. by inoculation. These bacilli differ from all other 

 micro-organisms by characteristic properties. 



The next step in the inquiry was one of essential im- 

 portance in determining the nature of the bacillus as the 

 materies morbi, viz. to isolate by successive cultivations 

 outside the animal body, the tubercle-bacilli, and having 

 thus completely freed them of all parts of tissue of the 

 tubercular deposit to introduce them into the system of 

 suitable animals. If these animals became afflicted 

 with typical tuberculosis, and if at the same time 

 similar animals kept under precisely the same condi- 

 tions, but not infected with the bacilli, remained perfectly 

 normal, it will be admitted that the exact proof has been 

 given that the bacilli constitute the cause of the tubercular 

 malady. 



All these conditions have been fulfilled by Dr. Koch in 

 an eminent degree. 



The tubercle-bacilli were successfully cultivated out- 

 side the body of an animal. Pure serum of blood of 

 sheep or cattle is sterilised by keeping it exposed in test- 

 tubes plugged with cotton wool, for six days daily for one 

 hour, to a temperature of 58 centigrades. After this the 

 serum is heated for several hours up to a temperature of 

 65 centigrades ; by this it is transformed into a solid 

 perfectly transparent mass, well adapted for the cultiva- 

 tion of the tubercle-bacilli. Such serum inoculated on 

 its surface under special precautions with tubercular 

 matter of any source — tuberculosis of man or animal, 

 spontaneous or artificially produced, and kept at a tem- 

 perature of 37 or 38 centigrades (i.e. about blood-heat) 

 for over a week, becomes gradually covered with peculiar 

 dry scaly masses ; these masses are the colonies of the 

 specific tubercle-bacillus. 



A minute particle of this crop is used for establishing a 

 second similar cultivation, this again for a third, and so 

 on. Tubercle-bacilli obtained in this manner, after 

 several successive generations, prove as effective in inocu- 

 lating animals with typical tuberculosis as fresh tuber- 

 cular matter. 



All animals susceptible to the malady that Koch inocu- 

 lated with these artificially cultivated bacilli, became in- 

 variably affected with the disease ; not one escaped ; 

 while other similar animals kept under precisely the same 

 conditions, except that they did not receive any tubercle- 

 bacilli, remained perfectly healthy. 



It is important to notice that the tubercle-bacilli re- 

 quire for their growth and multiplication a temperature 

 of at least 30 centigrades, and, consequently, they are 

 limited to the animal body, unlike the bacillus that pro- 

 duces splenic fever or anthrax, which is capable of multi- 

 plication at ordinary temperatures, as low as 20 centigrades, 

 and even less. 



The expectorated matter of tubercular patients is gene- 

 rally charged with tubercle-bacilli, and these often contain 

 spores. And it is probably through the presence of such 

 spores that that matter retains for a long time its infective 

 properties. Koch made experiments on guinea-pigs with 

 such sputa after having been kept dry for fourteen days, 

 for four weeks, and for eight weeks, and he found that in 

 all instances the sputa had retained their full virulence. It 

 is therefore just to assume that such sputa, even when 

 dried on linen, clothes, or even distributed with the dust 

 of the room, may be a source of infection. 



The practical importance of the discoveries of Koch 

 must be patent to everybody. In the recognition of the 

 tubercle-bacilli as the>//.f et origo of this terrible pest of 

 the human race— according to statistics quoted by Koch 

 one-seventh of all deaths being caused by tuberculosis — 

 in the recognition of the presence of these bacilli in the 

 sputa of tubercular patients, and in the tubercular deposits 

 of cattle afflicted with Perlsucht, we have at once become 

 supplied with the knowledge of the most common manner 

 of how tuberculosis may and probably is spread, as well 



