110 THE AMERICAN MONTHLY [May, 



but they also find application in the opposite direction, namely, in 

 preserving perishable articles from becoming decomposed. Meats, 

 vegetables, and fruits are kept from spoiling in various ways. 



i . They can be heated up to a temperature which kills the the bacteria, 

 and then sealed up so as to prevent any bacteria from getting in. 

 This method is employed in the ordinary process of canning. The 

 meats, vegetables, or fruits are put into cans, which are then heated up 

 to the boiling point of water or higher, and then sealed up. In actual 

 practice the cans containing the meats or other contents are nearly 

 sealed before they are heated, all except a small opening in one end, 

 which is closed with a drop of solder after the cans have been heated 

 long enough to kill the bacteria. But instead of sealing the substances 

 up in cans they can be preserved by stopping up the vessel containing 

 them with cotton, as with a tube of rutrient agar. Most bacteria are 

 killed by a temperature much below the boiling point of water. Still, 

 certain sorts of" bacteria have the power of forming so-called spores 

 which are very resistent. It has been recently discovered that there are 

 several kinds of bacteria in the ground which form spores so resistent 

 that they can be boiled several hours without being killed. 



2. Meats, vegetables, etc., are also preserved by drying. This needs 

 no further explanation, for moisture is essential to the growth of micro- 

 organisms. 



3. The addition of certain substances which are injurious to bacteria 

 is also often employed. Concentrated solutions of salt, that is to say,' 

 brine, prevents the growth of bacteria. Other substances, such as 

 salicylic acid, copperas and a great number of other things either kill 

 bacteria or prevent their growth, and consequently may be used as 

 preservatives. The most effectual of all is corrosive sublimate. The 

 great objection to this method of preserving substances for food is that 

 most of the germicides, as they are called, are injurious to health, and 

 many of them are very poisonous. Of course this objection does not 

 hold in the case of brine. 



4. Articles are preserved on ice, but generally for a short time only, 

 as this is an expensive method. It is hardly worth while to explain the 

 principle of this method, that bacteria require warmth in order to grow. 

 The study of bacteria has thus led to a clearer understanding of the 

 way in which the food is prepared for the higher plants on the one 

 hand, and the preservation of perishable articles on the other. It has 

 led to the prevention of many infectious diseases of animals and plants 

 and an improvement in wine making and brewing. 



The Botanical Preparations of Walter White. 



By CHAS. W. SMILEY. 



Though not pretending to take the place of objects mounted in the 

 usual way, yet, being enclosed in a transparent envelope, they are 

 available for immediate examination, either without or with magnifica- 

 tion — in many cases even with the higher powers of the microscope. 



Many of these preparations will be found figured in Strasburger's 

 ';' Hand-book of Practical Botany," as well as in " Thome's Text-Book " 

 and " Sach's Hand-book." 



Strasburger says: "■The study of vegetable structure is especially 

 favorable as an initiation into the use of thjs microscope ; and any one 



