56 ANNALES DE I/INSTITUT PASTEUFl 



pliological characterislics unimpaired as long as they retained 

 their motility. Thcso " young forms", as I may call them, 

 are very much shorter than the others, the smallcst being 

 from 3 to 4 [x in length and showing only 2 or 3 ciirves. 

 They are homogeneous and highly refractile and are usually 

 very motile; when stained they take the colour evenly and 

 deeply. Exainples of thèse forms are drawn in figure II, 

 n°' 8-14. 



The following day, or, days, typical large forms are seen in 

 abundance, as well as young forms and others intermédiare 

 between the two. 



In the course of several such experiments I hâve seen this 

 second crop of spirocheetes disappear more or less completely 

 and, six or seven days later, ihere followed a répétition of the 

 events I bave briefly described above. In other words, 

 regular relapses appear to take place in the body of the tick, as 

 regards the appearance and disappearance of the spirochœtes, 

 just as in the oase of the warm-blooded host. 



In stained spécimens of thèse young forms of spirochaetes, 

 both in the earlier^and in the récent séries of experiments, 

 some hâve been seen which were in apparent connection vvith a 

 chromatin granule or clump of granules, suggesting to my 

 mind a possible development of such a spirochaete from the 

 granule. In the récent work with dark-ground illumination a 

 careful watch bas naturally been kept for the occurrence of 

 such forms aiid in four ticks, two of them members of the 

 same batch and the other members of différent batches and 

 différent experiments, I bave observed the lorms drawn 

 in fig. I, n«' 7-21 and in fig. II, n°* 1-7. 



It will be seen from thèse sketches that many forms bave 

 been observed, from the apparent extrusioa of a short, highly- 

 refractile tail from the granule clump (fig. I, n**' 7-10) up to 

 typical spirochaete forms showing numerous and regular curves. 

 The forms figured were, with hardly an exception, in active 

 movement at the time of their observation, the longer ones 

 showing the characteristic rotatory and bending movement of 

 the ordinary blood-forms. The observations were made on 

 the tluids of the tick or on freshly crushed tissues suspended 

 in a drop of normal sait solution, the slides being immediatly 



