COEEESPONDENCE. 149 



liatclied. We trust that the several operations in the changes of the 

 ovum have been carefully watched. 



Lr. Pettigrew's New Appointment. — We are glad to learn that 

 Dr. J. Bell Pettigrew, F.R.S., has been apj)ointed Lecturer on Phy- 

 siology at the School of Medicine, Surgeons' Hall, Edinburgh. Dr. 

 Pettigrew is well known by his able researches into the structure of 

 the heart and stomach and by his valuable investigations of the organs 

 of flight in animals, and his recent lectiu"es on the apparatus of the 

 circulation. We congratulate the school and the lecturer on the 

 appointment. 



A Chair of Normal and Pathological Histology has been 

 foimded by the Spanish republican government in the University of 

 Madrid, and, according to the ' Medical Eecord,' endowed with a salary 

 of 5000 pesetas (210Z.). The medical faculty of the University of 

 Valencia has protested against the establishment of a similar chair 

 in that institution, on the grounds, inter alia, that the subjects are 

 already taught by the several professors. 



"What is the Thread Blight ? — At a recent meeting of the Eoyal 

 Horticultural Society, the Eev. M. J. Berkeley stated that he had 

 provisionally referred the thread blight which had attacked the tea 

 plantations in India to Cortidum repens Berk. 



A New Slide for the Microscope. — At a late meeting of the 

 American Philosophical Society Mr. Holman exhibited a slide for 

 the microscope, designed for tlie better observation of substances sus- 

 pended in fluids, especially the diflferent corpuscles of the blood. 

 The slide contained two concavities on its face, which were connected 

 by a groove, and covered by a thin plate of glass. It was highly 

 sensitive to changes of temperature. 



COEEESPONDENCE. 



Eeply to the Note in July Numbee, headed " Infoemation 

 eequieed as to miceoscopic powees." 



To the Editor of the ' Monthly Microscopical Journal.^ 



WATLA>irD, New York, U.S., July 25, 1873. 

 SiK, — With your permission I will ofier a few remarks by way of 

 reply to the questions of H. H., in the July number of the ' Monthly 

 Microscopical Journal,' page 39. 



However important the first question may be, it is one which it is 

 extremely difficult at the present time to answer. Considerable 

 margin must be left for error in any estimate that may be made of the 

 dimensions of the most minute particles of matter. The smallest 



