Using this assumption as a framework, this article will seek to identify changes in individual Glock cosmetic and design features and identify their sequence in the model history. While a strict serial number sequence is an inexact assumption, an accurate time line of importation for serialized firearms can be dated through records available from Glock.
Glock Serial Number Format
Around 1990 & about half-way through the two-letter serial number ranges, Glock started importing the models 20 (10mm), 21 (.45 ACP), 22, and 23 (both .40 S&W). By this time, the Austrian proof marks and the 17/19 mold mark were no longer present. The models 22 and 23 are essentially the .40 S&W versions of the 17 and 19 respectively; however, the more powerful cartridge forced a design change that added an additional pin to retain the locking piece in the frame. Some rare & early versions of these pistols may not have had the additional (3rd) pin. The models 20 and 21 were the first of the wide frame sizes made to accommodate the 10mm Auto and .45 ACP cartridges, respectively. All of these models are 2nd generation or later with both locking block pins in their design.
Prior to reaching the end of the two-letter serial number ranges, a second line was added to the upper cartouche on the grip of the pistol which now read: MADE IN AUSTRIA / GLOCK, INC., SMYRNA, GA.
Shortly after the change from two-letter to three-letter serial numbers, a second line was added to the lower cartouche on the grip with two additional patent numbers. The next internal upgrade in this approximate chronology was angled cuts made to the interior of the frame to relieve the back two corners where the locking piece sits. Without this modification, those two corners were prone to the initiation of vertical cracks in the polymer due to the repeated impact of the corners of the metal locking piece to the frame. The relief cuts seemed to prevent the occurrence and could also be added to older models after the cracks had begun (essentially removing the cracks in the process of making the cuts at their location).
The list of generation 2 changes above can be described sequentially based on the assumption of the serial numbers being sequential although this may not strictly be true. A more accurate description would be to say the changes listed here occurred during a watershed period during the middle of the second generation. The change from black internal parts to silver upgrade parts, the locking piece relief cuts, and the addition of a second line of text of the lower cartouche are all relatively contemporary changes roughly coinciding with the change from the two-letter to three-letter serial number range. Also in this time frame, the spring and guide rod assembly was upgraded to a one piece unit.
Studies on the microbiota of wild birds are rare or limited to a small number of animals, and those addressing the prevalence of Enterobacteriaceae are especially focused on certain groups, such as seagulls. More specifically, research on passerines covered outbreaks with high mortality, which provides no information on the prevalence of pathogens in apparently healthy animals. Thus, the role of these birds as reservoirs of bacterial pathogens may indeed be underestimated.1414 Benskin CM, Wilson K, Jones K, Hartley IR. Bacterial pathogens in wild birds: a review of the frequency and effects of infection. Biol Rev Camb Philos Soc. 2009;84:349-373.
A susceptibility test was performed with 70 isolates of E. coli, Klebsiella spp. and Salmonella spp., from 54 birds using the minimum inhibitory concentration assay (MIC) in agar and broth to determine the lowest concentrations of different antimicrobial drugs. Each one was evaluated in a serial dilution according to the protocol described by the Clinical and Laboratory Standards Institute (CLSI)2020 CLSI (Clinical and Laboratory Standards Institute). Performance Standards for Antimicrobial Susceptibility: Twenty-second Information Supplement - Document M100-S23. Wayne, PA: Clinical and Laboratory Standards Institute;2013. with ampicillin, ceftriaxone, ceftiofur, tetracycline, sulfamethoxazole/trimethoprim 19:1, chloramphenicol, gentamicin, nalidixic acid, ciprofloxacin, enrofloxacin, and nitrofurantoin. The following reference strains were used for the quality control of the antimicrobial susceptibility test: Staphylococcus aureus ATCC25923, Pseudomonas aeruginosa ATCC27853, Enterococcus faecalis ATCC29212 and E. coli ATCC25922.
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