April 28, 1882.] 



• KNOWLEDGE - 



547 



cause. Prior to Koch it had been placed beyond doubt 

 that the disease was lommunicalil'' ; and the aim of 

 the Berlin physician has been to determine the precise 

 character of the contaj;iuin which previous experiments 

 on inoculation and inhalation had proved to be capable of 

 indefinite transfer and reproduction. He subjected the 

 diseased organs of a great number of men and animals to 

 microscopic examination, and found, in all cases, the 

 tubercles infested with a minute, rod-shaped parasite, 

 which, by means of a special dye, he dill'erentiated from 

 the surrounding tissue. It was, lie says, in the highest 

 degree impressive to observe in the centre of the tubercle- 

 cell the minute organism which had created it. Trans- 

 ferring directly, by inoculation, the tuberculous matter 

 from diseased animals to healthy ones, he in every instance 

 reproduced the disease. To meet the objection that it was 

 not the parasite itself, but some virus in which it was 

 imbedded in the diseased organ, that was the real con- 

 tagium, he cultivated his bacilli artificially, for long 

 periods of time, and through many successive gene- 

 rations. With a speck of matter, for example, from a 

 tuberculous human lung, he infected a substance prepared, 

 after much trial, by himself, with the view of affording 

 nutriment to the parasite. Here he permitted it to grow 

 and multiply. From this new generation he took a minute 

 sample and infected therewith fresh nutritive matter, thus 

 producing another brood. Generation after generation of 

 bacilli were developed in tliis way, without the intervention 

 of disease. At the end of the process, which sometimes 

 embraced successive cultivations extending over half a year, 

 the purified bacilli were introduced into the circulation of 

 healthy animals of various kinds. In every case inocula- 

 tion was followed by the reproduction and spread of the 

 parasite and the generation of the original disease. 



Permit me to give a further, though still brief and 

 sketchy, account of Koch's experiments. Of si.x guinea- 

 pigs, all in good health, four were inoculated with bacilli 

 derived originally from a human lung, which, in fifty-four 

 days, had produced five successive generations. Two of 

 six animals were not infected. In every one of the infected 

 cases the guinea-pig sickened and lost flesh. After thirty- 

 two days one of them died, and after thirty-five days the 

 remaining five were killed and examined. In the guinea- 

 pig that died, and in the three remaining infected ones, 

 strongly pronounced tubercular disease had set in. Spleen, 

 liver, and lungs were found filled with tubercles ; while 

 in the two uninfected animals no trace of the disease was 

 observed. In a second experiment, six out of eight guinea- 

 pigs were inoculated with cultivated bacilli, derived ori- 

 ginally from the tuberculous lung of a monkey, bred and 

 re-bred for ninety-five days, until eight generations had 

 been produced. Ever)- one of these animals was attacked, 

 while the two uninfected guinea-pigs remained perfectly 

 healthy. .Similar experiments were made with cats, rabbits, 

 rats, mice, and other animals, and, without exception, it 

 was found that the injection of the parasite into the animal 

 system was followed by decided, and, in most cases, \-irulent 

 tubercular disease. 



In the cases thus far mentioned inoculation had been 

 effected in the abdomen. The place of inoculation was 

 afterwards changed to the aqueous humour of the eye. 

 Three rabbits received each a speck of bacillus-caMuTe, 

 derived originally from a human lung atTectcd with 

 pneumonia. Eighty-nine days had been devoted to the 

 culture of the organism. The infected rabbits rapidly lost 

 flesh, and after twenty-five days were killed and examined. 

 The lungs of every one of them were found charged with 

 tubercles. Of three other rabbits, one received an injection 

 of pure blood-serum in the aqueous humour of the eye, 



while tlie other two were infected, in a similar way, with 

 the same serum, containing bacilli derived originally from 

 a diseased lung, and subjected to ninety-one days' cultiva- 

 tion. After twenty-eight days the rabbits were kill< d. 

 The one which had received an injection of pure serum 

 was found perfectly healthy, while the lungs of the tvo 

 others were found overspread with tubercles. 



Other experiments are recorded in this admirable essay, 

 from which the weightiest practical conclusions may be 

 drawn. Koch determines the limits of temperature 

 between which the tubercle-ia«7/!f« can develope and 

 multiply. The mininnim temperature he finds to be 86° 

 Fahrenheit, and the vwxiviuin 104°. He concludes that, 

 uidike the bacillus anthracis of splenic fever, which can 

 flourish freely outside the animal body, in the temperate 

 zone animal warmth is necessary for the propagation of the 

 newly-discovered organism. In a vast number of cases 

 Voch has examined the matter expectorated from the lungs 

 01 persons aftected with phthisis, and found in it swarms of 

 bacilli, while in matter expectorated from the lungs of 

 persons not thus afflicted he has never found the organism. 

 The expectorated matter in the former cases was highly 

 infective, nor did drying destroy its virulence. Guinea- 

 pigs infected ^vith expectorated matter which had been 

 kept dry for two, four, and eight weeks respectively were 

 smitten with tubercular disease quite as virulent as that 

 produced by fresh expectoration. Koch points to the 

 grave danger of inlialing air in which particles of the 

 dried sputa of consumptive patients mingles with dust of 

 other kinds. 



It would be mere impertinence on my part to draw the 

 obvious moral from these experiments. In no other con- 

 ceivable way than that pursued by Koch could the true 

 character of the most destructive malady by which humanity 

 is now assailed be determined. And, however noisy the 

 fanaticism of the moment may be, the common sense of 

 Englishmen will not, in the long run, permit it to enact 

 cruelty in the name of tenderness, or to debar us from the 

 light and leading of such investigations as that which is 

 here so imperfectly described. 



PHOTOGRAPHY FOR AMATEURS. 



By A. Brothers, F.RA.S. 

 PART IV. 



IT is not at all necessary that the amateur should make 

 collodion — it can be purchased of many makers, of 

 excellent quality. If bought in small quantities it will be 

 ready for use, but if a pint or more be procured, the collo- 

 dion and iodizing solutions should be kept separate, and a 

 few ounces mixed a day or two before required for use. 



The glass plates and collodion being ready, we have ne.xt 

 to consider the " bath," as the solution of nitrate of silver 

 is called. The same term is also applied to the vessel used 

 to contain the silver solution. This vessel may be of glass, 

 porcelain, or vulcanite, or it may be of varnished wood, in 

 the form called a " well-bath," but glass should have the 

 preference — there are objections to each of the others. The 

 capacity of the vessel being ascertained — say 20 ounces 

 of water — that quantity should be placed in a bottle, 

 and 1^ ounces of re-crystallised nitrate of silver 

 should be added, and allowed to dissolve. The water 

 used should be distilled, or if that cannot be obtained, 

 rain water may be substituted. This silver solu- 

 tion requires to be iodized, that is a weak solution of 

 iodide of ammonia or potassium must be added, a few 

 drops onl)', or, which will answer equally well, a plate 

 coated with collodion may be left in the solution for a 



