ARTIFICIAL PROPAGATION^ OF TROUT. 71 



development of white spot. Twelve of the fishes experimented upon that 

 showed a growing white spot were examined and all showed severe bacterial 

 infection. Several kinds of bacteria were involved, one of which seemed iden- 

 tical with one of the forms observed in natural infections. However, all of 

 them were apparently effective in the destruction of the yolk. Similar infec- 

 tions were also observed in the eggs of landlocked salmon which had been 

 subjected to the same treatment. 



The difficulty of making exact bacteriological tests is apparent, since the injec- 

 tion of any pure cultures into healthy eggs will also cause the wound that 

 opens a pathway for the general bacterial fauna in the water. The use of sterile 

 water in the hatching operations of such experimental eggs would, of course, 

 solve this difficulty, but practical difficulties in the use of such water have here- 

 tofore made these tests impossible. 



Sufficient data is furnished by the observations and experiments set forth, 

 however, to indicate that bacteria are not to be regarded as primary agents in 

 the common form of white spot. That various bacteria are instrumental in 

 the disintegration of the yolk is not to be doubted, but the yolk must be re- 

 garded only in the light of so much inert organic matter which, once deprived 

 of its protective covering, is open to the attack of all saprophytic and holophytic 

 bacteria. It is a rupture of the yoke envelope that furnishes the primary 

 cause, and only the growth and spread of the spot is due to the bacteria. 



Periblast activity. — The white spot cases involving bacteria furnish only one 

 group, a group which, peculiarly enough, does not seem as large in numbers 

 as that which is now to be discussed. In these cases the most careful micro- 

 scopic scrutiny revealed no indication of bacteria, although the disintegration 

 phenomena do not differ materially. The most remarkable feature is fur- 

 nished by the periblastic cells. They are found throughout the disintegrating 

 region, augmented in number as compared witli normal eggs and embryos, but 

 extremely active, judging from their lengthened form. It may be repeated that 

 diseased eggs are generally found side by side with healthy ones. The affec- 

 tion is therefore not transmissible to normal eggs, and periblastic action just 

 as much as bacterial infection must have the ground prepai-ed for it by another 

 factor, which is therefore the primary agent. Eggs showing such periblastic 

 activity were obtained from Hartsville, Mass. ; Saratoga, Wyo. ; La Crosse, 

 Wis. ; and St. Johnsbury, Vt. Those from the two last-named points had under- 

 gone railroad transportation. The Saratoga occurrence was attributed by the 

 superintendent of that hatchery to chilling of the freshly stripped eggs, some- 

 thing which might also have taken place in the case of the Hartsville eggs (the 

 weather was cold at the time of egg taking), although no definite data was 

 obtainable. It was of some significance that the eggs from La Crosse showed 

 cases of bacterial infection, other cases wherein periblasts alone were active, 

 and, finally, a few cases that showed bacteria and periblasts side by side in the 

 disintegrating yolk. If mechanical disturbance was instrumental in introduc- 

 ing bacteria, and if it consisted in actxial rupture of the yolk envelope, it could 

 not have been responsible for the periblastic activity. In other words, since 

 the bacteria involved were undoubtedly present at La Crosse, a rupture should 

 give access to bacteria in one case as well as in another. Mechanical injury 

 without rupture of the envelope — that is, shock or concussion — is then left as 

 a possibility. An attempt was made to duplicate the conditions produced through 

 concussion by dropping a wooden box containing 200 landlocked salmon eggs 

 from a height of 3 feet. Two hundred normal eggs were kept for control. At 

 the end of 10 days 10 of the former lot showed indications of white spot, while 

 6 showed it in the control, a difference of 2 per cent. This is certainly not 

 significant enough to admit of any conclusions, save that eggs at that stage 

 of development (immediately before hatching) are extremely resistant to con- 

 cussion. A repetition of the experiment with younger eggs is therefore nec- 

 essary, especially in view of the fact that experience has proved the early 

 stages more susceptible to injury of any kind. 



Unfortunately no experiments could be conducted in connection with the 

 possible effect of chilling and freezing the eggs. The temperature factor is 

 liable to be very important in clearing up the periblastic activity, and there 

 should be little difficulty in the future in working out the relations. 



The necessity of more experimental data is thus plainly apparent. Sufficient 

 evidence is available, however, to point to physical injury of some kind as the 

 causative agency of the common occurrence of white spot. It seems more or 

 less of a truism to recommend more careful handling of fish eggs, but such a 

 recommendation points only toward the greatest possible elimination of dis- 

 tance shipments at pi-esent. Although so crude at the first glance, the " bulk " 



