52 
Philippine Journal of Science 
1920 
injury in the lung would seem to us to depend upon one, or a 
combination, of three factors: 1, The number of infesting 
worms ; 2, their physiology — that is to say, the character of the 
substances, if any, eliminated by them in the lung and the 
general nature of their life there; 3, foreign matter, such as 
bacteria from the intestinal tract possibly brought in by them. 
In the human host it will likely be somewhat difficult to ascertain 
these facts. 
In the feeding experiments carried out on lower animals in 
which lung symptoms such as pneumonia were seen to accom- 
pany the migration of the larval forms through the lungs, large 
numbers of eggs were administered in nearly every case and 
the resulting infections were, of course, correspondingly heavy. 
Furthermore, while fatal pneumonia is a frequent concomitant 
of early Ascaris infection in pigs, it must be remembered that 
the feeding habits of pigs are of a nature such as necessarily to 
bring about exceedingly heavy infections with any organism 
whose portal of entry is the alimentary tract. 
Do human beings acquire the massive single infections with 
Ascaris that attend the above circumstances? We are inclined to 
believe that they do not. It must be admitted that hundreds of 
ascarids have been found in the intestinal tracts of human beings 
in individual cases, but in these instances it seems to us that the 
total number represents the accumulation of many successive 
infections and not a single massive infection. Therefore, it is 
to be supposed that the number of larval forms passing through 
the human lung at any given time is probably insufficient to 
give rise to serious trouble there as a result of purely mechanical 
irritation or injury to the tissues. If the observations of those 
who have reported pulmonaiy symptoms in man in the course 
of an early Ascaris infection are to be relied upon, we probably 
must seek the cause of the trouble in some other factor, and 
therein would seem to lie the basis of some interesting work for 
the future. 
This introduces, of course, the question of immunity in Ascaris 
infections. It is held by some writers that a degree of immunity 
develops following an initial infection. The experiments of 
Yoshida(58) in connection with this are inconclusive, but cast 
doubt on the proposition. Yoshida quotes Stewart who claims 
to have immunized a rat by one infection with Ascaris larvae. 
In a series of observations now being carried on by one of us 
