240 P, MANSON ON THE PERIODICITY OF 



we ascertain what the subtle influence is that sets these creatures 

 circulating in thcblood stream and arrests them with such " mili- 

 tarj punctuality," we probably would let new light in on many an 

 obscure problem both in physiology and pathology. It was with the 

 intention of providing myself with a standard with which to com- 

 pare the results of observation and experiment that I prepared the 

 cliart I send you. If it is published it may help others, who are 

 willing to work on this subject, but who may not have the oppor- 

 tunities of the continuous observation it records. 



Dr. Mortimer Granville's ingenious speculations are based on the 

 assumption that the phenomenon of periodicity depends in some way 

 on sleep, either on the mechanical changes in the circulation when 

 the body is in the recumbent position, or in the different propor- 

 tions of oxygen in the blood, or in relative alterations of blood and 

 tissue temperatures during the walking and sleeping states. Now, 

 as the embryos begin to ai:»pear hours before the usual time for re- 

 pose, and are in no way sensibly affected by changes in the hours of 

 sleeping and waking, it is evident that the power which fixes them 

 and lets them loose operates independently of the sleeping state. It 

 is associated with the advent of night, but not of sleep. 



Part of Dr. Mortimer Granville's note is so much to the point 

 that I will quote it — " The change of place may be fairly ascribed to 

 change of state. Looking at the habits of life in the lowest 

 organisms, it can scarcely be supposed that the periodicity can de- 

 pend on the state or requirements of the filari^e. It is not likely 

 that the parasite needs repose, or that it resorts to special localities 

 to feed. It seems more probable that the state of the circulating 

 fluid determines the presence or absence of the filarias in the main 

 current by night and day respectively." . . . The first part of this 

 I quite agree with, but the latter part I am not quite so sure about. 

 What is the difference between the state of the circulating fluid at 

 4 p.m. and 6 p.m. respectively ? It is evident that something hap- 

 pens between these hours which liberates the embryos. I do not 

 know that physiologists have demonstrated or even supposed some 

 sudden change beginning in the blood between these hours. Again, 

 the conditions permitting the free circulation of the parasites con- 

 tinue with increasing effect up to midnight, and the restraining in- 

 fluences which fix them are gradually reapplied from that time till 

 they effect also complete fixation by nine or ten o'clock next fore- 

 noon. What alteration in the pliysiological state of tiie blood or 



