250 



SCIENCE. 



[N. S. Vol. III. No. 59, 



less strongly sculptured than when found in 

 southern waters, and on these geographical 

 variations a large number of species had been 

 founded. Most of these are merely varieties of 

 well-known Mississippi basin forms ; a few have, 

 perhaps, developed into good species; He be- 

 lieved these changes had all been wrought since 

 the close of the ice age. 



Similar changes on a larger scale had ap- 

 parently taken place in the closely related 

 unione fauna of the Atlantic drainage system, 

 which, he believed, had been for the most part 

 derived from the fauna of the Mississippi Valley, 

 though at an earlier date. 



M. B. Waite described the Life History of the 

 Pear-blight Microbe, Bacillus amylovrous. The 

 Bacilli first attack the blossoms and other new 

 growth in spring. They multiply in the nectar 

 of the blossoms and are able to enter the tender 

 tissues of the nectar disk without a puncture. 

 The germs are spread with great rapidity in the 

 orchards during blossom time by bees and other 

 insects. New infections take place on the tips 

 of growing twigs or on newly opened leaf buds 

 as well as on the blossoms, and may occur at 

 any time that new growth is pushing out. 



The majority of cases of blight come to a 

 standstill after running their course, the twigs 

 dry up and the germs all die in a week or two 

 of exposure to summer weather, for this Bacillus 

 forms no spores and cannot withstand drying. 

 Some of the cases of blight do not, however, 

 come to a standstill but continue slowly through 

 the summer. Again, late growth in autumn 

 often results in new infections, so that the trees 

 go into their winter condition with active germs 

 in them. These cases keep the Bacilli alive, and 

 the speaker had been unable to find the germs 

 living over winter in any other way. These 

 cases of ' hold-over ' blight are the key to the 

 pear-blight question, for by cutting them out 

 and destroying them when the tree is in a 

 dormant or semi-dormant condition we can ex- 

 terminate the microbes and prevent or cobtrol 

 the disease. 



Pierre A. Fish spoke of the Action of Electricity 

 upon Nerve Cells, stating that Hodge's experi- 

 ments have shown that certain well-defined 

 changes occur in the structure of the nerve cell 

 as a result of the stimulation of the nerves by 



weak electric currents. A strong current, on 

 the contrary, such as is used in electrocutions, 

 seems to cause no visible change, apparently 

 killing and fixing the protoplasm in a manner 

 analogous to that produced by histological re- 

 agents. 



He gave the results of the examination of 

 nervous tissue from three electrocuted subjects i 

 In No. 1 a portion of the myel was examined, 

 particularly the motor cells, and the cytoplasm 

 in most cases showed numerous vacuoles. In 

 No. 2 normal cells were the rule, and vacuoles 

 the exception in the cervical myel. A small 

 portion of the cortex from the precentral gyre 

 (the region nearest the electrode) showed vacuo- 

 lation of the large and small pyramidal cells, 

 either in the cell body, or in the peripheral 

 process. In No. 3 a small portion of the cere- 

 bellum only was obtained, and after careful 

 search vacuoles were found in two Purkinje 

 cells. 



As vacuolation of the nerve cell is often the 

 result of disease, an examination of plenty of 

 material and a knowledge of the previous his- 

 tory of the individual is essential for a solution 

 of the question of the action of electricity. 



C. Hart Merriam read by title a Revision of 

 the Lemming- Voles {genus Synaptomys). 



Mr. Vernon Bailey read a paper entitled 

 Tamarack Sivamios as Boreal Islands. He stated 

 that the common Eastern tamarack {Larix 

 americana) is generally considered a boreal 

 tree. East of the Rocky Mountains it over- 

 reaches the Boreal Zone, and occurs in scattered 

 swamps throughout the transition and even in 

 the northern part of the Upper Austral Zone. 

 Such swamps are common in central Pennsyl- 

 vania, northern Ohio, southern Michigan and 

 northern Indiana, though the line marking the 

 southern limit of the Boreal Zone is drawn 

 much farther north. Within a radius of ten 

 miles from Ann Arbor, Mich., which is in the 

 Upper Austral Zone, are at least a dozen such 

 swamps, ranging in size from a few acres to a 

 mile square. 



The vegetation of these sw'amps is composed 

 largely of boreal species of plants, including the 

 white birch, cassandra, andromeda, cranberries, 

 pitcher plants, many species of northern grass, 

 carex, herbaceous plants, mosses and a carpet 



