Jeffries.] 
48 
[May 7, 
those inoculated with the culture grown in heat will live ; the oth- 
ers will all die. This is not a lone example ; there are many forms 
of bacteria which undergo like metamorphoses, as the bacillus of 
chicken cholera, and swine plague and rabbit septicaemia, perhaps 
identical with the first, swine erysipelas and false charbon, also 
certain bacteria of fermentation. This cannot be ascribed to in- 
dividual change not transmitted, since in several of the cases the 
plant multiplies in the body, and again in cases the plant after be- 
ing weakened in virulence can be cultivated without reversion under 
conditions where its virulence is maintained. Koch has thus kept 
a variety of anthrax for two years. 
Some may object that since many of the species of bacteria mul- 
tiply only by division, all are really only separated parts of one 
organism and think that the spore would not vary. This is not 
the case ; the spores have the grade of virulence of the culture in 
the case of anthrax. Certainly the individuals grown from spores 
must be regarded as distinct descendants ; indeed, those produced 
by simple division must be so regarded, or the whole of the large 
and variable group of non spore-forming bacteria regarded as one 
being, a reductio ad absurdum. 
It is customary to class this loss of power-virulence next to death, 
a sort of partial death. Perhaps it may be, and certainly is pro- 
duced by conditions which if too intensely forced produce death ; 
but in this case we have the strange phenomenon of a dying organ- 
ism propagating its kind in the same stage of death for a great num- 
ber of generations. Making the small allowance of two generations 
a day, at the end of two years Koch would have had the 1460th 
generation. 
Whether such harmless forms varieties can be altered back into 
virulent ones is doubtful. Pasteur, on inoculating animals in a 
series, from the most susceptible up, got positive results, but Koch 
in a second effort failed. 
Many will doubtless be inclined to reject the “ weakened ” kinds 
on the ground that the difference is physiological. It must, how- 
ever, be borne in mind that form is nothing but the result of the 
processes of growth ; that is, the result of physiology : that the mass 
of recognized characters of bacteria are physiological, that the form 
is often the result of the nutrient on which the bacteria grow. 
We thus see that of Lamarck’s laws the first is of such a nature 
as to be incapable of proof and not compatible with the present 
