G. H. F. Nutt all 
65 
for variable periods of time before they were examined microscopically 
or used for inoculation purposes after being crushed. 
In four experiments, the lice were killed 2-4 days after the infective 
meal; these lice showed no spirochaetes, and they were not infective. 
In three experiments, the lice were killed 5-6 days after the infective 
meal; these lice showed no spirochaetes, but they were infective. Five 
lots of lice, killed after 10-12 days, showed spirochaetes but none 
were infective. Exceptions occur, however, with regard to the time 
when the lice become infective and cease to be so. Thus, in two experi¬ 
ments by Nicolle, Blaizot and Conseil (previously referred to), some lice 
were found infective on the ninth day, but in this case the sjhrochaetes 
are stated not to have attained their full size, and Nicolle and Blanc 
have found lice to be infective for a man on the third day (one experi¬ 
ment) and for a monkey on the 15th day (one experiment). 
If we combine these interesting results of Nicolle and his colleagues 
with those of Sergent and Foley, previously cited, they may be 
tabulated as follows: 
Spirochaetes Infectivity 
Lice on days 2-5 after an infective meal absent inconstant 
„ day 6 „ ,, „ absent constant 
,, days 8-9 „ „ „ inconstant exceptional 
Therefore the infectivity of the lice does not depend upon the presence 
in them of microscopically visible spirochaetes. Lice usually become 
most infective about the sixth day, just before the spirochaetes reappear 
in them. Their infectivity subsequently diminishes, and it vanishes 
when the spirochaetes are constantly present and have attained their 
full size. Lice may occasionally be infective as early as the third and 
as late as the 15th day after feeding on infective bipod. 
Nicoile and Blanc reach substantially the same conclusions as 
Sergent and Foley. They.believe that the spirochaetes in man and in 
the louse, after attaining their full dimensions, dwindle in size, and 
become no longer recognizable as spirochaetes. The minute forms are 
the only ones that are infective and capable of multiplication. It is 
doubtful" if the fully grown spirochaetes undergo division either length¬ 
wise or crosswise as has hitherto been believed. 
Nicolle and Conseil (20. i. 1915, pp. 18-20) state that the intra¬ 
venous administration of arseno-benzol, ludyl, or galyl, causes the 
spirochaetes to disappear in a few hours. We would add that Ehrlich 
was the first to discover that arsenic (salvarsan) exerts an immediate 
specific curative effect on relapsing fever. 
Parasitology x 5 
